1. Field of the Invention
The present invention relates to a connection structure, and particularly to a connection structure of a contact portion in a conductive-member construction in which heavy current flows.
2. Description of the Related Art
In order to realize high integration of a semiconductor device such as IC or LSI, a technique in which wiring is mutually conducted between elements formed in a multi-layered structure with high density is very important. Conventionally, in order that electric connection be made between elements formed in a multi-layered structure and electrically isolated by an interlayer insulating film, and between wirings, and also between an element and a wiring, for example, a via hole structure in which electric connection is made for elements or wirings, which are formed in layers at upper and lower sides of an interlayer insulating film, with conductive materials being embedded in through holes formed in the interlayer insulating film, or connection structures as shown in FIGS. 8A to 8C, 9A and 9B are employed.
FIGS. 8A, 8B, and 8C show an example of a connection structure of two wirings, which extend in directions perpendicular to each other and are formed in a layered form via an interlayer insulating film 34. An end of a first wiring 30 provided as a lower layer and an end of a second wiring 32 provided as an upper layer are connected via a through hole.
This connection structure is obtained in such a manner as will be described below. First, as shown in FIG. 8B, the interlayer insulating film 34 is formed by a CVD method on the first wiring 30, and thereafter, a rectangular hole is formed in the interlayer insulating film 34 at the end of the first wiring 30 so as to become a through hole 16. As shown in FIG. 8C, an extension wiring 32 is formed on the interlayer insulating film 34 so as to cover the through hole 16.
FIGS. 9A and 9B show an example of a connection structure of a diffusion layer 35 provided in a substrate 20 and an extension wiring 11d. As illustrated in the plan view of FIG. 9A and in the cross-sectional view of FIG. 9B, a through hole 16 is provided in an interlayer insulating film 34b formed by a CVD method or the like on an entire surface of the substrate 20 in which the diffusion layer 35 forming semiconductor elements is formed, so as to expose the diffusion layer 35. An extension wiring 32b having a connection region 31 which covers the through hole 16, is provided on the interlayer insulating film 34b. 
A through hole contact 18 (for example, see FIGS. 8A, 8B, 8C, 9A, and 9B), that is a portion in which electric connection is made between such elements, and between wirings, and also between an element and a wiring and is a bottom surface portion of the through hole, is formed in such a manner that electric current is apt to concentrate therein. In order to obtain a semiconductor device having higher reliability than a conventional one, it is important to prevent increase of current density due to concentration of electric current in the through hole contact. For this reason, it becomes important to use materials having a low resistance and good ohmic properties in a region of the through hole contact or to provide a structure in which no local concentration of electric current occur.
Accordingly, there has conventionally been proposed a method in which an area of the through hole contact is increased by increasing a transverse dimension of a wiring disposed as a lower layer or by increasing the size of a through hole, so as to reduce current density. For example, in a case of Emitter-Coupled Logic (ECL) circuit, electric current flows between the lower-side wiring and the upper-side wiring via the through hole contact in a unit from several tens of mA to several hundreds of mA. Therefore, the transverse dimension of the wiring and the size of the through hole are each made relatively larger to become several tens of xcexcm to several hundreds of xcexcm so that an allowable current density becomes about 1xc3x97305 (A/cm2) or less.
However, in a conventional multi-layered wiring structure having a through hole contact, there exists a problem in which local concentration of electric current is caused and so-called electromigration such as void or hillock thereby occurs.
For example, in the structure in which the first wiring 30 at the lower side and the second wiring 32 at the upper-side are connected together so as to be made perpendicular to each other as shown in the plan view of FIG. 8A, in a case in which electric current flows from the first wiring 30 to the second wiring 32, assuming that the length of each side of the through hole contact 18 is indicated by xe2x80x9clxe2x80x9d, a distance between an end of the second wiring 32 to one side of the through hole contact 18 is indicated by xe2x80x9cmxe2x80x9d, a distance between an end of the first wiring 30 to one side of the through hole contact 18 is indicated by xe2x80x9cnxe2x80x9d, positions on the first wiring 30 at which straight lines drawn from corners of the through hole contact 18 perpendicular to a side of the second wiring 32 cross the side of the second wiring 32 are indicated by xe2x80x9cA1xe2x80x9d and xe2x80x9cA3xe2x80x9d, a position at a midpoint of positions A1 and A3 on the first wiring 30 is indicated by xe2x80x9cA2xe2x80x9d, and a position on the second wiring 32 where a straight line drawn from a corner of the through hole contact 18 nearest the above-described positions A1, A2, and A3 perpendicular to a side of the first wiring 30 crosses the side of the first wiring 30 is indicated by xe2x80x9cBxe2x80x9d, a length of a shortest path of current flowing from each position A1, A2, and A3 to the second wiring 32 can be expressed artificially as described below.
|A1B|=m+n+1xe2x80x83xe2x80x83(1)
|A2B|=m+n+(1/2)1xe2x80x83xe2x80x83(2)
|A3B|=m+nxe2x80x83xe2x80x83(3)
wherein, |A1B| indicates a length of a shortest path between point A1 , and point B, |A2B| indicates a length of a shortest path between point A2 and point B, and |A3B| indicates a length of a shortest path between point A3 and point B.
The relation |A1B| greater than |A1B| greater than |A1B| is given by the abovedescribed expressions (1), (2), and (3), and therefore, the path indicated by A3B is the shortest. Accordingly, it is considered that electric current concentrates in one corner of the through hole contact 18 on the path of A3B.
If current concentrates, void or hillock may be generated at a high frequency, and there is a high possibility that after a fixed period of time has elapsed, electromigration may occur to cause improper wiring. Particularly, as shown in FIG. 8C, in a case of a wiring structure including a through hole, a layer thickness of a wiring in a region which covers a side surface portion of the through hole is small, and therefore, there is also a possibility that a thin layer portion of the wiring is molten and broken by occurrence of electromigration or generation of heat due to concentration of current.
Further, in a case of the structure shown in FIGS. 9A and 9B, current is apt to concentrate in a side surface portion of the through hole disposed perpendicular to a direction in which current flows. In this case as well, the layer thickness of a wiring in a region which covers the side surface portion of the through hole is small, and therefore, there is a possibility that a thin layer portion may be molten and broken due to occurrence of electromigration or generation of heat.
In view of the above-described circumstances, it is an object of the present invention to provide a connection structure in which concentration of current is prevented in a portion in which wirings, or an element and a wiring are connected.
In order to achieve the above-described object, in accordance with a first aspect of the present invention, there is provided a connection structure in which two conductive members formed at upper and lower sides of an insulating film are electrically connected with each other, wherein a path changing portion is formed in a vicinity of a connecting portion of the two conductive members and changes a path of a portion of current flowing in the conductive members to disperse a current path.
In the first aspect of the present invention, a current path is dispersed due to a portion of the current path being changed by the path changing portion, and therefore, concentration of current in a region in which current is apt to concentrate from a structural point of view is prevented. As a result, occurrence of electromigration such as void or hillock, which is caused by concentration of current, or melting and breakage of wiring can be prevented. xe2x80x9cThe two conductive members formed at upper and lower sides of the insulating filmxe2x80x9d mentioned in the present invention includes not only wirings, but also includes any two members which need be electrically connected with each other, for example, an element and an extension wire.
In a second aspect of the present invention, the path changing portion is an insulating portion which prevents passing of a portion of current so as to keep away from a position in which a current path concentrates in the connecting portion of the two conductive members. An insulating material for forming the insulating portion is not particularly limited, but various known materials such as SiO2 or air can be selected.
For example, when air is selected as the insulating material, a structure in which a slit is formed in the conductive member is provided. In this case, no cost for forming the path changing portion is required and the above-mentioned structure can be formed in a relatively simple process, which is preferable.
In order that the slit be formed in the conductive member, according to a third aspect of the present invention, when the two conductive members are disposed so as to extend in different directions, the path changing portion is comprised of at least one slit formed along a direction in which current flowing in at least one of the conductive members flows, and is provided in a vicinity of a position in an internal angle formed by the two conductive members.
In this structure, when a plurality of slits are formed, as the path changing portion, in one conductive member, so long as the plurality of slits are arranged in such a manner that intervals thereof are made larger as a distance from a position near an internal angle formed by two conductive members becomes longer, flow of current becomes more smooth as a distance from a position in which flow of current concentrates becomes longer, which is preferable.
In accordance with a fourth aspect of the present invention, when the two conductive members are disposed so as to extend in the same direction, the path changing portion is comprised of at least one slit formed to be inclined to a direction in which current flowing in a conductive member at an upstream side flows, and is provided in the conductive member at an upstream side in a vicinity of the connecting portion.
In the above-described structure, preferably, the slits may be disposed symmetrically with respect to a central axis of a conductive member at an upstream side so as to change a portion of current flowing in the conductive member at an upstream side from the direction of the central axis of the conductive member to the direction of an exterior side of the conductive member.
Further, according to a fifth aspect of the present invention, there is provided a connection structure in which two conductive members formed at upper and lower sides of an insulating film are electrically connected with each other, wherein a connecting portion of the two conductive members is formed such that flow of current becomes more smooth as a distance between the connecting portion and a position in which flow of current concentrates becomes longer.
Namely, the current path is changed and current is made to flow in a region in which current flows smoothly. Therefore, as described in the fifth aspect of the present invention, there is provided a structure in which current is hard to flow in a position in which flow of current concentrates, and flow of current becomes smooth in a position in which no concentration of current flow occurs. In this case, the current path is dispersed without being concentrated in one portion, and therefore, occurrence of electromigration such as void or hillock, which is caused by concentration of current, or melting and breakage of wiring can be prevented.
For example, current is hard to flow in a small-sized through hole and current flows smoothly in a large-sized through hole, and therefore, according to a sixth aspect of the present invention, the connecting portion is comprised of a plurality of through holes, and the plurality of through holes are disposed in such a manner that dimensions thereof becomes larger as a distance between a through hole and a position in which flow of current concentrates becomes longer.
A film thickness of a conductive member for covering a side surface portion of the through hole is made small, and therefore, a resistance of the conductive member for covering a side surface portion of the through hole becomes larger than that of other portion of the conductive member and current flows more smoothly in a portion having no through hole formed therein as compared with a portion having the through hole formed therein. Accordingly, in a seventh aspect of the present invention, the connecting portion is comprised of a plurality of through holes, and the plurality of through holes are disposed in such a manner that intervals of the through holes become larger as a distance between a through hole and a position in which flow of current concentrates becomes longer.
Further, in accordance with an eighth aspect of the present invention, there is provided a connection structure in which two conductive members formed at upper and lower sides of an insulating film are electrically connected with each other, wherein a connecting portion of the two conductive members is comprised of a through hole having a side surface which is inclined to a direction in which current flowing in a conductive member at an upstream side flows.
In other words, as described above, the film thickness of the conductive member for covering the side surface of the through hole is made smaller than that of other portion of the conductive member, and therefore, a density of current flowing through the side surface portion increases and concentration of current occurs at a high probability. In the eighth aspect of the present invention, the side surface of the through hole is inclined to a direction in which current flowing in the conductive member at an upstream side flows, and therefore, current is received by a large area as compared with a case in which the side surface of the through hole is made perpendicular to the direction in which current flows. When current flows through the side surface portion, the current density increases. As a result, occurrence of electromigration such as void or hillock, which is caused by concentration of current, or melting and breakage of wiring can be prevented.
Moreover, according to a ninth aspect of the present invention, there is provided a connection structure in which two conductive members formed at upper and lower sides of an insulating film are electrically connected with each other, wherein a connecting portion of the two conductive members is comprised of a through hole which is formed so as to expose at least upper and side surfaces of the conductive member formed at a lower side.
Namely, in the ninth aspect of the present invention, the through hole formed in the insulating film to allow connection between the upper conductive member and the lower conductive member is provided so as to expose not only an upper surface portion of the lower conductive member, but also expose at least two surfaces, that is, upper and side surfaces of the conductive member. For this reason, an area for the connection becomes larger, and even if concentration of current occurs when current flows through the connecting portion, current is received by a large area. As a result, there is no possibility of increase in current density, and occurrence of electromigration such as void or hillock, which is caused by concentration of current, or melting and breakage of wiring can be prevented.